Separation of coal.



. DEGD.

F. W. C. SCHNlEWIND E M. SCHNlEWlND. EXECUTRIX.

SEPARATION OF COAL.

APPLICATION FILED JAN- 20. m3.

Patented Sept. 7, 1915.

930% twaooao ('1 Homm rEEnEErc W. o. scnivmwrnn, or ENGLEWOOD, NEW JERSEY; ELMA M. soHnIEwmn EXECUTRIX or SAID FREDERIC w. o. SCHNIEWIND, DECEASED.

snrnnn'rron or conn Specification of Letters Iatent.

Patented Sept. 't, 11915.

Application filed January 20, 1913. Serial no. 743,185.

To all whom it may concern:

Be it known that I, FREDERIo W. C. SCHNIIEWIND, a citizen of the United States, residing at Englewood, in the county of Bergen and State of New Jersey, have mvented certain new and useful Improvements in the Separation of Goal, of which the following is a specification.

This invention relates to the separation or purification of coal;'and it comprises a process of purifying coal from gangue and other impurities, or of separating different kinds of coal from each other, wherein the coal is so treated as to bring out or develop the difference in hygroscopicities of the different constituents of the coal, and thereafter subjected to electrostatic separation.

It also comprises such a process of purification or separation wherein coal, and particularly bituminous coal, in a pulverulent condition is first purified and separated from inorganic impurities, and particularfy those ..of a conductive nature such as pyrites and pyritical gangue or slate, by electrostatic fifrmeans and the purified or partially purified coal thereafter moistened to develop the difference in hygroscopicities of the various ingredients of thecoal, and the moistened coal is tlien separated by electrostatic means.

It further comprises such a process of purification or separation wherein pulverulent coal containing undesirable constituents,

such as mineral charcoal, of arela'tively more friable nature, is first purified from the finer particles of the more friable constituents by screening or pneumatic means, or otherwise, before the development of the hygroscopicities and the electrostatic separation.

It further comprises such a process of a0 purification or separation wherein coal is first dried to remove any excess moisture andto increase the hygroscopic properties of the coal before the subsequent moistening and development of such hygroscopicities; 5 and it further comprises certain modifications of such a process, and combinations thereof with other coal treating and purification processes; all as more fully hereinafter set forth and as claimed.

Goal, as it occurs in nature, and as mined,

contains varying, amounts of inorganic material such as slate or gangue and pyrites more or less intimately distributed throughout i:ts mass. Many coal veins also consist of strata of different kindsof coal intermixed or interlaminated so that, the mined coal is not homogeneous, even when obtained from the same mine and vein, but is made up of different coal constituents too intimately intermixed to be readily separated. Many bituminous coals, in particular, are of this nature, being made up of layers or mixtures of harder and of softer coal, or of lustrous and dull coal, or of coking and non-coking coal, or of purer and less pure (bone coal or slate) coal, etc.

For coking purposes the coal should be as pure as possible and relatively free from ash and sulfur (pyrites) and also from coal which is non-coking in its nature. The non-coking constituents, if present, make the coke resulting of inferior value. Among the different constituents of bituminous coal may be mentioned the shiny lustrous coal (called in German glanzlcohle) which is generally the purest coal and has the best coking quality; the dull coal (called in German mattlcohle) which possesses generally a higher percentage both of ash and of volatile matter but which is generally of poor coking quality; the cannel and pseudo-cannel coals; and mineral charcoal (faserkohle). The mineral charcoal in particular is of a friable nature and has no coking quality whatever. During the mining operation the larger lumps and pieces of slate are removed, but the finer particles of impurities and those in timately distributed throughout the coal still remain. The mining operation, on the other hand, serves to mix the various lumps and layers of coal found in vproximity to each other so that thev are even more extensively intermixed than before mining. Such run-of-mine coal, if too high in ash cannot be used economically for industrial purposes where a low-ash coal or coke is necessary. Also, as indicated above, coal containing too large an amount of non-coking coal, is of inferior value for coking purposes. I

In my application Serial No. 737,689, filed December 19, 1912, I have described and claimed a process of purifying or separating coal from such impurities as are of an electrostatically conductive nature or as are united to' particles of an electrostatically conductive nature by disintegrating the coal sufiiciently to separate the particles of con ductive pyrites or gangue as muchas possible from the coal particles and subjecting the thus disintegrated coal to electrostatic separation whereby the conductive particles are repelled and separately collected from the coal particles. --This process is of value particularly for removing pyrites and py ritical gangue from pulverulent coal and thus reducing its sulfur and ash content.

The present invention relates to a process of purification or separation based on the difference in hygroscopicities of the different constitutents of coal intermixed with each other. Some of these difleren't constitutents have been enumerated above, particularly the different kinds of coal found in bituminous coal mixtures. Many of these different kinds of coal and of the constituents of the same kind of coal vary materially in their physical character and in their hygroscopicity. Thus where lustrous and dull coal occur in the same vein, the lustrous coal may in one case show the greater hygroscopicity while in another case the reverse may be true. 'In general lustrous coal is erally very low e; g. 1.2%.

more hygroscopic than dull coal; but to this.

.air, may amount to more than 20%. Again 1n bituminous coals the absorption of Water or hygroscopicity may vary, for example, between 2 and 7.5%, although it is usually nearer the lower figure than the higher. Different constituents of the same vein such as lustrous and dull coals may show differ ences of as much as 1 to 1.5%, or even more in their hygroscopicity under the same conditions. Mineral charcoal which may alsobe present mixed with other kinds of coal is a very undesirable constituent, particularly of coking coals. Its hygroscopicity is genages of water content or hygroscopicity for convemence of reference have been given as those possessed-by the coals at 15 C. It'

will of course vary somewhat with the temterature of the coal and the humidity of the atmosphere to which the coal has been exposed,'as well as vary with different coals and the above descript ons are given merely as specific illustrations ofthe varying hy- These percentof water upon their surfaces. The amount and speed ofadsorption or condensation will of course depend on the moisture content and temperature of the surrounding air or gas in cases where the coal is exposed to such air or gas, but it nevertheless varies to a greater or less extent in difi'erent kinds of coal under the same conditions, due apparently other things being equal, to the varying surface attraction inherent in the different kinds of coal.

According to the present invention coals containing in intermixture different constituents possessing different hygroscopicities are treated to develop such differences, and then subjected to electrostatic separation whereby the coal possessing the greater hygroscopicity and particularly the greater amount of condensed or mechanically retained water on its surface is repelled to a greater extent than the less hygroscopic coal other things being equal, and separation thus effected. If the coals already possess such differences of moisture content that the selective acti'onof the electrostatic separation is able to effect their separation, they may be separated without further treatment after suitable disintegration. Such a condition, however, seldom arises. Usually the coal must be first reduced in size andthen moistened immediately before the separation takes place, or if the coal is already too moist it may be'partly dried to develop the difference in electrostatic susceptibilities and then separated electrostatically.

Coal from wet mines, or coal which is not sufficiently dry, may require to be first dried, and with other coals it is sometimes more advantageous to give the coal a preliminary drying before moistening since by drying the moisture contained in the interior of the particles may be removed, the exterior or surface moisture being most effective for electrostatic separation.

In cases where the coal also contains a large amount of pyrites and gangue it can be with advantage first subjected to electrostatic separation to reduce or remove such conductive impurities. By such a preliminary purification not only is the content of sulfur (pyrites) and pyritical gangue decreased, but complications which might otherwise arise subsequently are minimized. For such particles if present would be repelled along with the more strongly repelled hygroscopic coal and effective separation might be thus rendered more diffigroscopicities of different kinds of coal. j cult; while by first removing the pyrites The property of greatest value for purposes of the present invention is the property of condensing moisture upon the surface of the coal particles or of mechanically holding moisture thereon. Different kinds of coal' possessing different hygroscopicities are capable of condensing varying amounts and gangue the subsequent separation of the greater and less hygroscopic coal proceeds more smoothly.

Previous to the electrostatic separation and to the development of the hygroscopicity the coal must be suitably reduced in size. The crushing may be of the run-ofmine coal, in one or more stages, to particles of a size suitable for electrostatic separation. Crushing to pass an -8-mesh sieve is usually necessary, and crushing to pass a 10 or 12 mesh screen may give even better results. Instead of crushing directly to this fineness, the coal can be screened to remove large lumps and only smaller sizes furthermay be graded by screening or by other methods of volumetric classification, or may be separated from the fine particles and dust by pneumatic means, etc. The more friable constituents such as mineral charcoal which is one of the softest of the bituminous coal constituents, and also one of the least desirable in coking coals, will tend to be crushed more readily and more finely than the harder and more valuable coal so that more of such constituents may be found in the fine coal dust and in the finer coal particles. In such cases the crushed coal can be advantageously screened to remove this fine powder or dust, or it can be subjected to pneumatic separation whereby the finer and lighter particles are removed with the blast of'air or other gas and separately collected, the coal being at the same time dried if a blast of warm or dry gas is used. Again screening for the purpose of removing the larger particles, and pneumatic treatment to remove the fine dust can both be used, the intermediate fraction or fractions only in such cases being subjected to electrostatic separation. These'fractions can be varied with different coals and only such fractions obtained by screening, washing, or pneumatic or other processes treated according to the present invention as the nature of the coal or the relation of coking and non-coking components may render advantageous. With coals containing mineral charcoal it may be advantageous to remove this constituent before the first electrostatic treatment. This carin many cases be readily effected by pneumatic means or by screening or separating as above described,

l'the fine dust being thus also removed, in-

eluding that of explosive fineness.

After the coal has been crushed, and after it has been subjected to such, preliminary drying, screening, separating or purl-- fying. processes as already described, in case such preliminary processes are necessary or advantageous, it is treated to develop the difference in the hygroscopicity of the different constituents. It is now in a granulated condition, and may also be free from fine dust, as already described, and it is advantageous that it should be so free, since the presence of fine dust inexcess may seri-' ously interfere with the moistening of the coal. It is also advantageous that the pyritesand pyritic'al gangue should have. been previouslyremoved as,.--a'lready indicated, and the process willbe described as applied to such a previouslypurified prod uct, although it willbe evident that other products can be similarly treated.

The moistening or development of the differences in hygroscopicities should ad- 'vantageously immediately precede the electrostatic separation. This moistening may be effected in different ways. It is necessary that a small amount of moisture only be added. This may be added by passing a current of moist air or gas through the granulated coal. The variety of coal having the higher hygroscopicity or the greater capacity. for surface condensation will ad sorb the water more readily and to a greater extent. The adsorption can be increased by increasing the water vapor content of the air to saturation or to the dew point, or by using coal at a temperature below the dew point of the air current used. Since some coals tend to oxidize readily even on exposure to moist air it is in some cases more advantageous to use a moist current of an inert gas such as flue gas, or better the products of combustion of coke oven gas or coal gas. Such waste gas contains a large percentage of hydrogen which burns to water and is present as water vapor in 1ts products of combustion. Oxidation during the moistening of the coal is thus prevented or minimized.

The water content of the waste gas can be increased by further addition of steam or water. Steam itself may in some cases be used, preferably diluted with air or an inert gas. The amount of moisture can be determined by the volume, temperature and moi'sture content of the gas passed over a given quantity of coal; also by the temperature of the coal. After the "difference in hygroscopicity has been brought out in the coal through the wet coal, or when it is slightly heated to remove the excess of water, the histrous greasy coal will be more readily dried,

and thereby differentiated. This moisture may be only mechanically retained and visible or it may be that more properly called hygroscopic moisturewhich is invisible. The more porous coals thus more readily absorb and holdNvater mechanically and through capillarity than do the harder smooth coals. Some grades of anthracite and their admixed slate show such diiferences. Also certain grades of bituminous coals contain intermixed impurities of a relatively more The further addition of oxygen to the coal p which readily takes-place with many coals porous nature.

Particularly when the coal resulting from the present process is to be used for coking it isadvantageous that-the coal be protected from oxidation during its preliminary treatment, since even atmosphere oxidation tends to lessen the coking qualities of the coal.

- when exposed to the air causes a decrease in the heat value of the coal in much the same manner as do ash and moisture since oxygen itself is also incombustible. Viewed from another standpoint the prevention of oxidation serves to protect the oxidizable constituents of the coal and to preserve these constitutents in an unoxidized condition in which they appear to be most valuable, particularly for coldng purposes. In order that this protection from oxidation may be as complete .as possible it is advantageous not only that the coal be protected from atmospheric om'dation' during its moistening but that it also be protected during the subsequent electrostatic separation as well as during the previous crushing, drying, screening, pneumatic treatment and other preliminary processes which may be carried out. Such protection can be readily efiected by the use of an inert atmosphere r readyf described, are; brought in contact th-anelectrostatically charged electrode .or surface the wetter particles or the par- 1. ticles containing-a arger amount of condensed water on their surface are more ffl strongly repelled than the drier particles and can thus be separated to a greater or less xtent from each other. It will beunyderst od, however, that this separation is not asharply defined one; since there is no ment.

sharp line of distinction between the different particles as respects their conductivity and their non-conductivity. The separation is rather of two materials of like nature between which, however, selective electrostatic difi'erentiation can take place.

In effecting the separationthe coal particles can be charged electrostatically and then passed through an electrostatic or combined electrostatic and electromagnetic field; or brought in contact with an electrostatically charged surface. Coal thus previously charged is repelled by an electrode similarly charged and attracted by one oppositely charged while coal which is not thus charged remains unaffected. In the case of coal particles with different moisture contents and hence difi'erent electrostatic capacities the more moist will tend to be more and the less moist less, affected by the electrostatic treat- The terms conductors andtnonconductors as applied to such a moistened coal mixture can be used only with their relative and not with their absolute signification.

If, the coal particles are not previously charged they may besubjected directly to an electrostatically charged electrode or surface charged 0. g. to 15,000 to 50,000 volts, and the particles which because of their greater water content are capable of being more readily charged will'be more readily repelled and can be thus separately collected,

The electrostatic separation of the present invention can be carried out in an explosion preventing atmosphere, or under explosion preventing conditions, but owing to the presence of added moisture, there is less danger of explosion with this process. The danger from explosion is further minimized by the previous removal of the fine dust and fine mineral charcoal. 4

It will be evident that the process of the present invention can be repeated in part or in whole with the same coal. Thus fractions resulting from a first treatment can be subjected to a second or third treatment, or they can be' subsequently again treated to develop their difference in hygroscopicity and again subjected to electrostatic separation. Such subsequent treatment may in clude only, moistening, or moistening preceded by drying to remove previously added moisture and increase the hygroscopici ty of the coal. 1

Goal to be used for coking purposes should advantageously .be as dry as possible. Water present in coal charged into a coke oven must be'vaporized before coking takes place thus lowering the temperature of the oven and requiring heat energy for its removal. "Where coal has been moistened in the manner above described it is accordingly sometimes advantageous to dry the coal bealready indicated. Thus the developmentof the hygroscopicities and the subsequent elec-' trostatic separationcan be preceded by drying, pneumatic purification, screening, and other processes of volumetric separation, etc. The electrostatic treatment for the elimination of the pyrites is particularly advantageous as a preliminary process in combination with the hygroscopic treatment and separation. The removal of fine particles ofdust or'of mineral charcoal or other more friable constituents e. g. by screening or pneumatically is also advantageous previous to the hygroscopic treatment and even previous to the first electrostatic treatment for the separation of pyritical gangue, etc. Other combinations than those herein de- I scribed can also be effected both supplemental to and in combination with the separation based upon hygroscopicity.

In the accompanying drawings is shown, diagrammatically, an arrangement wherein can becarried out the process of the present invention including the preliminary treatment of the coal to remove the conductive constituents (pyrites) and the subsequent moistening or development of the differences of hygroscopicities of the different coal constituents followed by; electrostaticseparation of the moistened coal. It will be understood, however, that the process is not dependent upon this particular type or arrangement of apparatus which is given merely for purposes of illustration.

The apparatus shown comprises a hopper 1, which in practice is provided with feed-. ing means (not shown) for insuring .an even and regular feed of the coal therefrom, a revolving roll or electrode 2 below the hopper outlet, a small wire electrode 3,incased in glass or wood, etc., connections 4: and 5 leading from the electrodes 2 and 3 respectively to a suitable source of electrostatic energy, an adjustable partition or division plate 6 below the roll 2 and slightly in front of the same, a brush 7 cit-acting with the roll for removing adhering particles therefrom, and an inclosing casing 8- provided with valved discharge outlets ,9 and 10 and with valved air or gas inlet and outlet connections 11 and 12. Below the outlet 10 and communicating with the same is a second hopper-15 similar to '1 but pro-- vided with inlet and outlet connections and 26, the lower of which leads from a suitable source (not shown) of moist gas or air, and the upper of which is connected with an eduction fan or other eduction means (not shown). Below the hopper 15 are roll 16 and electrode 17 provided with wire connections 18 and 19 respectively, partition 20 andbrush 21, all similar in their structure and arrangement to the corresponding elements of the upper casing. A lower surrounding casing 22, is also provided, having valved discharge outlets 23 and 24.

In this apparatus the present proc'ess can be carried out as follows, the description being rather by way of illustration than of limitation. The coal in a crushed and granulated condition and freed from the fine mineral charcoal and the fine coal dust, and also,

if necessary from any excess moisture, is

charged into the hopper 1. Generally the coal is screened and only a particular size treated at once, 6. g. between 4 and S mesh,-8

' and 16 mesh, 16 and 60 mesh, etc. The coal is fed from the hopper lina thin stream on to the roll 2 where the more conductive particles are charged and repelled and thus separated from the less conductive coal, the conductive particles (pyritic'al gangue, etc.,) falling to the outside of the partition 6 and being discharged through the outlet 9 while the less ,condu'ctive coalfalls inside the partition 6 and into the outlet 10 from which it falls into the hopper 15. The casing 8 Surrounding the upper electrostaticapparatus isprovided with inlet and outlet connections 1;]. and 12 by means ofwhich a current of a are ing, or explosion-preventing, or non-oxidizing gas canbe passed through the casing,

and the coal undergoing separation ma n-' tained under drying, explosion-preventing, or non-oxidizing, or all three, conditions, as desired and as more fully described in my prior application Ser. No. 7 37 ,689. The hopper 15- is connectedQby means of the inlet pipe 25 with a source of. moist gas which may advantageously be theproducts of combustionof coke oven gas, which contain a large amount of water vapor resulting from the combustion of the hydrogen of the coke oven gas burned. "The outlet 26 from the hopper 15 is provided with a fan or other means not shown of securing circulation of the gas through the hopper. By regulating the velocity of the moist gas relative to the flow of coal through the hopper, a greaterlor less amount of moisture can be'condensed' upon the coal particles and the difierence in hygroscopicities of the coal constituents can thus be developed, the time required depend ing both on the rate of flow of the gas and on the difference in temperature of the gas and coal; also' upon the degree of saturation of upon, the coal has been already described in /d etail, and it. is not deemed necessary to do "so again in connection with the specific form of apparatus illustrated. From the hopper 15 the moist coal is fed on to the roll 16 and separation of the more moist and more conductive coal constituents from the less conductive effected in a manner similar to that already described in connection with the upper apparatus, the more and less conductive portions being separately collected and removed through the outlets 23 and 24. There results from this specific process described four different fractions or portions of the coal, viz,the'-.fi ne coal dust and mineral charcoal remov ed before the coal reached the hopper 1 the rejected fraction, usually small in amount and high in ash and sulfur discharged from the casing 8 through the outlet 9; and the two'coal fractions obtained in the lower casing 22 and discharged through the outlets 23 and 24, and varying in amount depending upon the differences in hydroscopicities of the different coal constituents.

The rejected portion obtained at 9 may be further treated to-separate impurities from the goal; and the fractions obtained at 231 and -24 can be used directly orfurther treated, as

already described more in detaiLj f i The foregoing description of' ithe 'apparatus illustrated and of the process as carried out in it is intended to be illustrative of .a specific I application of 'the;-,;'i nvention. Variations in this apparatusjand specific process, and modifications of the. same and combinations with other processes can'be made, asmore fully hereinbefore indicated,

- and such modifications and combinations are included the limits of the accompanying claims.

I claim: p

,1. The process of separating coal from granulated coal mixtures which comprises moistening the coal to develop the differences in hygroscopicities of the different constituents of the mixture, and subjecting the moistened coal to electrostatic separa- 1 2. The process of separating coal from tion.

coal WhlCh comprises crushing the mixture to such. an extent that particles of different constituents of the mixture possessing different hygroscopicities are. separated from. each other, developing the difference in hygroscopiclties .of such coal particles by moisteningthe same while still in-a freshly b crushed conditionland subjecting the moistened "coal. mixture to electrostatic separation; 3. The process of separating coal from "coal mixtures which comprises crushing the coaL-subjecting the crushed coal to electrostatic separation to separate therefrom 'con-.

This action of the, moist gas ing the thus moistened ductive pyritical impurities, developing in the resulting coal the difference in hygroscopicities of the different constituents by moistening the same and subjecting the moistened coal mixture to electrostatic separation.

4. The process of separating coal from oping in the resulting coal. the difference in hygroscopicities of the different constituents by moistening the same, andsub ectlng the moistened coal to electrostatic separatlon.

6. The process of separating coal from granulated coal mixtures which comprises drying the coal, moistening'the dry coal to develop the difference in hygroscopicities of the different coalconstituents, and subjecting the moistened coal to electrostatic separation.

7. The process of separating coal from granulated coal mixtures which comprises moistening the coal to develop the difi'erence in hygroscopicities of the different constituents of the mixture by passing therethrough a current of moist gas, and subjecting the moistened coal to electrostatic separation.

. 8. The process of separating coal from granulated coal mixtures which comprises moistening the coal to develop the difference vin hygroscopicities of the different constit-. uents of the mixture by passing there-- uents of the mixture, and subjecting the thus moistened coal to electrostatic separation.

10. The process of separatln coal from granulated coal mixtures'whic comprises condensing moisture'upon the surfaces of the coal particles to-develop the difference in hygroscopicityof the different constit-' uents of the mixturelby passing there-' through current of moist s, and subjectcoa to electrostatic separation. i v i 11. The processof separatin coal from granulated coal whic comprises moistening the coal to develop the difference in hydroscopicities of the different constituents of the mixture, subjecting the moistened coal to electrostatic separation, and maintaining the coal during such treatment under substantially non-oxidizing conditions.

12. The process of separating coal from coal mixtures which comprises crushing the mixture to such an extent that particles of different constituents of the mixture possessing differenthygroscopicities are separated y from each other, developing the difference in in hygroscopicities of the different 'kinds of,

coal contained in the mixture, and subjecting the moisture mixture to electrostatic separation.

14. The process of separating the various constituents of bituminous coal mixtures and of removing therefrom mineral charcoal which comprises crushing the coal, separating from the crushed coal the finer particles including the finer particles of the mineral charcoal, moistening the mixture to develop therein the difference in hygroscopicities 'of the different constituents of the mixture and sub ecting the moistened coal to electrostatic separation.

15. The process of separating the various constituents of bituminous coal mixtures and of removing pyritical impurities therefrom which comprises crushing such coalto forma granulated mixture, subjecting such mixture to electrostatic separation to remove conductive pyritical impurities, developing in the thus purified coal the difference in hygroscopicities of the coal constituents by moistening the same, and subjecting the moistened mixture to electrostatic separation.

16. The process of separating the various constituents of bituminous coal mixtures and of removing mineral charcoal and pyritical impurities therefrom which comprises crushing such coal to form a granulated mixture, separating from the crushed coal the finer particles'includingthe finer particles of the mineral charcoal, subjecting the mixture to electrostatic separation to remove the conductive pyritical impurities, developing in the thus purified coal the difference in hygroscopicities of the coal constituents by moistening the same, and subjecting the moistened mixture to electrostatic separation.

17. The process of treatingcoal containing coal constituents of the same or substantially the same density butof different coking qualities which comprises crushing the coal to pass a 4-mesh screen, sizing the coal,

into fractions of the same or substantially the same size,and treating each fraction electrostatically to separate said coal constituents from eachother.

18. The process of treating moist coal containing coal constituents poss'esSingdifi'erent hygroscopicities which comprises partially drying the moist coal until different hydroscopic conditions are developed in the different constituents, and subjecting the resulting coal in a granulated condition to electrostatic separation.

In testimony whereof I affix my signature in the presence of two witnesses.

FREDERIG W. G. SCHNIEWIND.

Witnesses:

ROBERT C. Mn'roALrE, HOWARD P. WITHINGTON. 

